Store each client's play queue in the database

The queue lived in memory and was shared by all clients, so a restart or a
finished sync cleared it. Every client now has its own queue in the new
queue and queue_song tables (added to the undeployed migration 000006).

The music endpoints return the queue ID in the X-Queue-Id header and expect
it back. A request without an ID, or with an ended one, starts a new queue.
/music/reset ends the queue and returns a new ID, and a sync ends all
running queues. Ended queues are kept as history.

The deprecated legacy routes without the /api/v1 prefix are removed.

internal/server/middleware/queue.go

@@ -0,0 +1,38 @@
+package middleware
+
+import (
+	"context"
+	"net/http"
+
+	"music-server/internal/logging"
+
+	"github.com/danielgtaylor/huma/v2"
+	"github.com/google/uuid"
+	"go.uber.org/zap"
+)
+
+// QueueHeader carries the client's queue ID in requests and responses.
+const QueueHeader = "X-Queue-Id"
+
+type queueKey struct{}
+
+// QueueID returns the queue ID resolved by Queue.
+func QueueID(ctx context.Context) uuid.UUID {
+	id, _ := ctx.Value(queueKey{}).(uuid.UUID)
+	return id
+}
+
+// Queue resolves the queue ID in the X-Queue-Id header with resolve, which starts a new queue
+// when the header is missing or the queue has ended. The ID is returned in the same header.
+func Queue(api huma.API, resolve func(context.Context, string) (uuid.UUID, error)) Middleware {
+	return func(ctx huma.Context, next func(huma.Context)) {
+		id, err := resolve(ctx.Context(), ctx.Header(QueueHeader))
+		if err != nil {
+			logging.GetLogger().Error("Failed to resolve queue", zap.Error(err))
+			_ = huma.WriteErr(api, ctx, http.StatusInternalServerError, "Internal Server Error")
+			return
+		}
+		ctx.SetHeader(QueueHeader, id.String())
+		next(huma.WithValue(ctx, queueKey{}, id))
+	}
+}